Antibodies are immunoglobulin glycoproteins having a basic unit of a monomer structure. The monomer is a Y-shaped protein that consists of four polypeptide chains, two of which are identical heavy chains and two are identical light chains connected by disulphide bridges. There are five different types of heavy chain (γ, μ, α, ε and δ) that distinguish the immunoglobulin classes (IgG, IgM, IgA, IgD and IgE, respectively). There are also two different types of light chain (λ and κ) resulting from different gene products.
IgG (a monomeric immunoglobulin approximately of 150 kD in size) provides antibody-based immunity against invading pathogens and, due to the high specificity that IgG has towards specific antigens within the body, it is the most commonly used reagent in immunological research and clinical diagnostics.
Monoclonal antibodies (herein termed Mabs) are antibodies that have identical specificity towards a single antigen and are generated from a cell line that has been produced from a single cloned cell. Mabs constitute the fastest growing sector in the biopharmaceutical industry where is it estimated that sales will reach $30 billion (US) by 2010. Antibody titres from mammalian cell cultures have continued to improve over the last 20 years and alternative downstream processes and chromatography adsorbents are required to resolve the process bottlenecks in the processing of Mabs.
Antibody fragments (parts of whole antibody molecules) offer several advantages over whole antibodies. They are easier and more cost effective to manufacture, they have fewer side-effects in patients, by reducing the risk of cytokine release and its associated toxicity, due to the absence of the Fc (heavy chain) region, and they can be modified to include therapeutic payloads. There are several types of antibody fragments that are either IgG′ domains prepared by specific endopeptidase enzyme digestion or that have been genetically engineered in cell lines. These include monovalent fragments such as Fab′, Fab and scFv; bivalent fragments such as F(ab′)2 diabodies and minibodies; and multivalent fragments such as triabodies and tetrabodies.
Many antibody fragment products are in development for use as therapeutics or in diagnostics. Recombinant antibody fragments are expected to have a significant share of the $6 billion (US) per year diagnostic market, from in vitro immunoassays to in vivo tumour and clot imaging applications (Holliger, P., & Hudson P. J., Nat. Biotech 23 (9; 2005) 1126-1136).
Most antibody fragment products lack a protein A-binding site and therefore, unlike full-chain antibodies, cannot be purified by protein A affinity chromatography. In most instances, conventional chromatography techniques are used to purify antibody fragments. Protein L, a protein with a molecular weight of 35000 Daltons derived from a bacterial species of Peptostreptococcus magnus, is known to bind to antibody light chains and has been investigated for the purification of some antibody fragments but is not considered to be cost-effective and is not available in commercial quantities.
WO97/10887 discloses triazine-based compounds, useful as affinity adsorbents, of formula I
wherein R1 is H, alkyl, hydroxyalkyl, cyclohexyl, NH2, phenyl, naphthyl, 1-phenylpyrazole, indazole, benzthiazole, benzoxazole or benzimidazole, any of which aromatic groups can be substituted with one or more of alkyl, alkoxy, acyloxy, acylamino, amino, NH2, OH, CO2H, sulphonyl, carbamoyl, sulphamoyl, alkylsulphonyl and halogen;
one X is N and the other is N, C—Cl or C—CN;
Y is O, S or NR2;
Z is O, S or NR3;
R2 and R3 are each H, alkyl, hydroxyalkyl, benzyl or β-phenylethyl;
Q is benzene, naphthalene, benzthiazole, benzoxazole, 1-phenylpyrazole, indazole or benzimidazole;
R4, R5 and R6 are each H, OH, alkyl, alkoxy, amino, NH2, acyloxy, acylamino, CO2H, sulphonic acid, carbamoyl, sulphamoyl, alkylsulphonyl or halogen;
n is 0 to 6;
p is 0 to 20; and
A is a support matrix optionally linked to the X-containing ring by a spacer.
Compounds of formula I are disclosed as having affinity for proteins such as immunoglobulins, insulin. Factor VII or human growth hormone.
Compounds of related structure are disclosed in WO00/67900 and WO03/097112. They have affinity for endotoxins.
Certain triazine-based compounds disclosed in WO97/10887 have affinity for immunoglobulins. An example of a compound showing such affinity is a compound of structure II

Compounds such as II are able to remove immunoglobulins specifically from complex mixtures or feedstocks such as human plasma.
Another type of commonly encountered feedstock is industrially produced cell culture supernatant, in which monoclonal antibodies are present at concentrations up to 5 g/l of supernatant. Compounds such as II may also be useful for specific removal of monoclonal antibody from these mixtures, although their performance is known to be compromised by the presence of cell culture additives such as Pluronic F-68.
Pluronic F-68 is an anti-foaming agent commonly used in mammalian cell culture. It is a block copolymer of polyoxyethylene and polyoxypropylene, and has a molecular weight of approximately 8000 Da. Pluronic F-68 is used to protect cells from shear and air bubble damage, and is typically used in an amount of 1 g/L in cell culture supernatants. Its presence may reduce or abolish the ability of compounds such as II to remove immunoglobulins from such feedstocks, which represents a considerable obstacle to the use of such ligands for direct capture of monoclonal antibodies from mammalian cell culture media.